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United States Patent |
5,013,394
|
Rolland
,   et al.
|
May 7, 1991
|
Method for detection of end of grinding of a thin layer magnetic head
Abstract
The invention concerns a method for the detection of the end of grinding of
at least one thin layer magnetic head, the head comprising, at the stage
of implementation of said method, an active face, formed by two magnetic
poles (1, 2) separated by a gap (4). The method comprises the following
steps:
deposition of a conductive layer (7) on the entire active face (3)
etching of the active face coated with said conductive layer;
deposition of a layer of dielectric material (8) on the etched active face;
grinding of the active face starting from the face that is free of the
layer of dielectric material (8) until total removal of that part of the
conductive layer (7) located above the gap (4), this removal being
detected by the sudden variation in resistivity between the two magnetic
poles (1, 2).
Inventors:
|
Rolland; Jean-Luc (Paris, FR);
Beguin; Jean-Yves (Paris, FR);
Magna; Henriette (Antony, FR);
Jacobelli; Alain (St Michel Sur Orge, FR);
Penot; Maurice (Palaiseau, FR)
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Assignee:
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Compagnie Europeenne de Composants Electroniques LCC (Courbevoie, FR)
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Appl. No.:
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381749 |
Filed:
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June 26, 1989 |
PCT Filed:
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October 21, 1988
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PCT NO:
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PCT/FR88/00518
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371 Date:
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June 26, 1989
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102(e) Date:
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June 26, 1989
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PCT PUB.NO.:
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WO89/04038 |
PCT PUB. Date:
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May 5, 1989 |
Foreign Application Priority Data
Current U.S. Class: |
216/22; 29/603.09; 29/603.16; 216/52 |
Intern'l Class: |
B44C 001/22; C23F 001/00; C03C 015/00; C03C 025/06 |
Field of Search: |
156/627,645,655,656,664,665,667
29/603
360/110,119,121,122,128,137
|
References Cited
U.S. Patent Documents
3495049 | Feb., 1970 | Humphreys et al. | 29/603.
|
3938193 | Feb., 1976 | Sargunar | 360/137.
|
4670972 | Jun., 1987 | Sakakima | 29/603.
|
Foreign Patent Documents |
2115211 | Sep., 1983 | GB.
| |
Other References
Patent Abstracts of Japan, vol. 10, No. 312, (P-509)(2368), Oct. 23, 1986,
& JP, A. 61122909 (Sanyo) Jun. 10, 1986.
|
Primary Examiner: Powell; William A.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt
Claims
We claim:
1. Method for the detection of the end of grinding of at least one thin
layer magnetic head, the head comprising, at the stage of implementation
of said method, an active face, formed by two magnetic poles separated by
a gap, the detection being obtained through the interruption of an
electrical circuit, characterized in that it comprises the following
steps:
deposition of a conductive layer on the entire active face to form said
electrical conduit;
etching of the active face coated with said conductive layer;
deposition of a layer of dielectric material on the etched active face;
grinding of the active face starting from the face that is free of the
layer of dielectric material until total removal of that part of the
conductive layer located above said gap, said removal being detected by
the sudden variation in resistivity between the two magnetic poles.
2. Method according to claim 1, characterized in that the grinding is of
the cylindrical type.
3. Method according to claim 1, characterized in that the grinding is of
the plane type.
4. Method according to claim 2, characterized in that the grinding of the
active face is achieved symmetrically with respect to said gap.
5. Method according to claim 1 characterized in that the thickness of the
layer of dielectric material is at least equal to the thickness of the
magnetic poles.
6. Method according to claim 1 wherein said conductive layer (7) is formed
by aluminium or chromium.
7. Method according to any of the claims 1 to 6, characterized in that said
layer of dielectric material is formed by alumina or silica.
Description
The present invention concerns a method for the detection of the end of
grinding of a magnetic head made according to the so-called thin layer
techniques.
Thin layer magnetic heads are made by successive deposits of magnetic,
dielectrical and conductive materials. These layers undergo final
operations for etching and grinding the magnetic poles.
The depth of the gap is a geometrical characteristic, the checking of which
is fundamental for magnetic heads and, especially, for those using
technologies for the deposition and etching of thin layers. In effect
whereas, in a massive magnetic head (VHS or audio head for example) or in
a head of the type having, on each side of the gap, a magnetic metal alloy
(also called a magnetic metal alloy in gap head), the efficiency hardly
varies with the depth of the gap (typically 0.05 dB/.mu.), this is not so
for heads using thin layer technologies (variation typically around 0.2
dB/.mu.). In the latter case, it proves to be necessary to perform very
precise controls on this dimension while making the head. Furthermore the
values of the depth of the gap differ greatly according to the
technological method used: they are of the order of 20 to 40.mu. for a
massive head and of the order of 2 to 10.mu. for a thin layer head. For
thin layer heads, this small depth causes a very appreciable reduction in
the section of the gap and, hence, a reduction in the thermal noise
related to the real part of the impedance of the head. For, the thermal
noise is proportionate to the section of the gap.
It is therefore very important to be able to perform, repetitive, reliable
and precise controls on the depth of the gap during the stage for
finishing the active face of the head. In order to achieve this result,
many methods are presently used by those skilled in the art. It is
possible, during the grinding step, to measure the impedance of the head
to adjust it to the desired value. It is also possible to detect the
opening of the magnetic circuit of the head by measuring the inductance at
the terminals of the coil. There are also optical methods for checking the
depth of the gap. All these methods are generally well mastered, but they
have major drawbacks: they are difficult to implement and the measured
values change constantly during the process of establishing the size of
the depth of the gap. The precision obtained is relatively low: about
0.5.mu. for a gap depth of the order of 2.mu..
In order to overcome these drawbacks, the invention proposes a method for
the detection of the end of grinding by measurement of the variation of a
signal, the sizing of the depth causing an all or nothing type of
variation in the signal. The variation in the signal comes into play at
the precise instant when the desired dimension is achieved.
The invention therefore has, as an object, a method for the detection of
the end of grinding of at least one thin layer magnetic head, said head
comprising, at the stage of implementation of said method, an active face,
formed by two magnetic poles separated by a gap, the detection being
obtained through the interruption of an electrical circuit, characterized
in that it comprises the following steps:
deposition of a conductive layer on the entire active face to form said
electrical circuit;
etching of the active face coated with said conductive layer;
deposition of a layer of dielectric material on the etched active face;
grinding of the active face starting from the face that is free of the
layer of dielectric material until total removal of that part of the
conductive layer located above said gap, said removal being detected by
the sudden variation in resistivity between the two magnetic poles.
The invention will be better understood and other advantages will emerge
from the following description, given as a non-restrictive example, and
through the appended figures, of which:
FIG. 1 shows a simplified structure of a planar head;
FIGS. 2 to 6 represent different steps of the method according to the
invention applied to the structure shown in FIG. 1.
The method according to the invention is based on the detection of the
passage from electrical conduction to electrical insulation during the
step of the method for fabrication of a magnetic head aimed at to
achieving the desired gap depth. It is assumed, in the method, that there
is electrical conduction between the two magnetic poles before the desired
depth is achieved and insulation when the desired dimension is achieved.
This method is especially well suited to thin layer heads made according
to a planar method. The thickness of the magnetic layer forming the poles
defines the depth of the gap.
FIG. 1 shows a simplified structure of a planar head to which the method
according to the invention can be applied particularly well. The active
face 3 of the magnetic head may have a thickness of between 1 and 40.mu..
It has a first magnetic pole 1 and a second magnetic pole 2 separated by a
gap 4. The active face 3 lies on a magnetic substrate 5 containing a
dielectric pad 6 located beneath the gap 4. The dielectric pad 6 is a
second gap with respect to the magnetic circuit formed by the parts 1, 2
and 5. The gap 4 is located somewhat in the center of the dielectric pad 6
which may have a thickness of about some tens to some hundreds of
micrometers. The constituent materials of this magnetic head are, for
example, a magnetic metal alloy (FeNi, FeAlSi, CoZrNb, etc.) for the
magnetic poles 1 and 2, a dielectric such as SiO.sub.2 or Al.sub.2 O.sub.3
for the gap 4. The dielectric pad 6 may be formed by glass or an epoxy
resin. The magnetic substrate 5 may be formed by a poly or monocrystalline
ferrite of manganese-zinc, namely a material with high resistivity. As an
example, the widths of the gaps 4 and 6 may be 0.2.mu. for the first gap
(or microscopic gap) and 200.mu. for the second gap (or macroscopic gap).
The planar structure shown in FIG. 1 then receives a deposit of conductive
material throughout the surface of the section. The thickness of this
deposit may range from some hundreds of angstroms to some tens of
micrometers. This conductive material may be a layer of aluminium or
chromium for example. FIG. 2 shows the previous planar structure covered
with a layer 7 of conductive material. Since the magnetic material forming
the poles 1 and 2 have high conductivity levels, they are also put into
electrical contact.
FIGS. 1 and 2 show only one magnetic head, but it is clearly advantageous
(and therein lies one of the characteristics of the invention) to make
several structures on a wafer.
The wafer on which these structures are made is then etched in order to
define the final geometry of the facing poles. FIG. 3 is a top view of a
structure of this type.
A dielectric material (alumina, silica, for example) is then deposited on
the entire structure. The thickness of this deposit is at least equal to
the thickness of the magnetic materials forming the poles. FIG. 4
illustrates this stage of the method. It corresponds to a section AA of
FIG. 3 and has, in addition, the layer 8 of the dielectric material.
Before depositing the layer 8, care will be taken to anticipate a
possibility of electrical connection with magnetic poles having low
resistivity (typically of the order 100.mu. cm.) These electrical
connections may be provided for at any time during the execution of the
method for making magnetic heads, but before the deposition of the
dielectric layer 8.
Depending on the use planned for these heads and the grinding method used,
all the heads, or only a restricted number of them, judiciously
distributed over the processed wafer, may be provided with these
connections.
With a view to clarity, the rest of the description will deal solely with
the finishing of a single head, i.e. its cylindrical grinding operation to
achieve the size of the gap. This head is provided with connection
contacts connected to each pole. The resistance measured between the poles
at this stage of the method is, therefore, very low.
The head then undergoes the final cylindrical grinding operation as shown
in FIG. 5. This grinding is done symmetrically with respect to the gap.
The dielectric layer 8 gradually takes on a cylindrical profile, and the
magnetic poles 1 and 2 also begin to be worked upon at their ends opposite
the gap 4. The resistivity between the poles varies only very little
during this grinding operation until the part of the conductive layer 7,
located above the gap, is in turn removed, as shown in FIG. 6. At this
point, the resistivity between the two poles suddenly becomes very great
and the grinding is stopped, the specified dimension having been achieved.
The detection of the sudden change in resistivity can be done by any means
known to those skilled in the art. A simple ohmeter is enough.
The method described herein for a separated head undergoing cylindrical
grinding can be adapted to plane grinding operations. It may be used to
set the dimension of the depth of the gap for several heads in group
processing operations. These heads would then be either in the form of
strips, or again, with the entire wafer. In these group processing
operations, only some judiciously chosen heads will have their resistance
between the poles measured.
The method according to the invention is a very simple means for detecting
the instructed size to be achieved. It is a method working on an all or
nothing basis, thus making it easy, to the utmost, to detect this
dimension, even with rudimentary means. The implementation of the method
according to the invention requires only one additional deposition step
during the method for making the heads. The connection of electrical
contacts on the poles depends on the final type of geometry planned for
the heads. Since the detection is very simple, it is no longer
indispensable for an operator to be present to assess the progress and
descent towards the instructed dimension and to take the decision to stop
the machine. The method can be very easily automated.
The dielectric layer 8 remains in certain places and, in particular, in the
etched parts of the magnetic poles, on each side of the gap 4, thus
preventing deterioration in the magnetic reading or writing medium.
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